1. Field of the Invention
The present invention relates to a rotatably supporting device adapted for use in correcting a balance of a rotating body, which can precisely correct a balance of a heavy rotating body by rotatably supporting in a floating state by a fluid.
2. Description of Related Art
In a rotating body, for example, an impeller of a turbine, an impeller of a compressor, a fly wheel, a wheel of a vehicle or the like, in order to remove any unbalance due to a tolerance during its manufacturing or assembling or the like, a balance-correction operation is conducted by singly rotating the rotating body to measure an unbalance amount and to correct the measured amount of unbalance.
With regard to the balance correcting method of the rotating body mentioned above, patent document 1 (Japanese Examined Patent Publication No. 4-40650) proposes a balance testing machine serving as a balance correcting device which can perform a balance correction by rotating a rotating body without using an auxiliary shaft and an auxiliary spindle at a time of the balance correction even if the rotating body is not provided with a specific support part.
In the balance testing machine 1, as shown in FIGS. 1A and 1B, a vibration bridge 4 is supported on a device stand 2 via a support spring 3, and a support journal 5 serving as a mandrel for rotation support is fixed to the vibration bridge 4 in a vertical direction.
A fluid supply hole 6 having a closed upper end portion is formed in a center portion of the support journal 5, a plurality of radial outflow holes 7 are provided to lie in upper and lower flat planes in a radial direction so as to be communicated with the fluid supply hole 6, and a compressible fluid such as an air or the like is supplied thereto so as to flow out thereof.
Further, a plate 8 is integrally provided perpendicularly to a lower end portion of the support journal 5, a plurality of auxiliary holes 9 are formed in the plate 8 so as to open on an upper surface, and are communicated by an internal annular flow path 10, and the compressive fluid such as the air or the like is supplied so as to flow out of the above-mentioned holes.
In the balance testing machine 1, a rotating body 11 is mounted onto the support journal 5 by inserting a hole 12 of the rotating body 11 to the support journal 5 and the compressive fluid such as the air or the like is flown from the outflow hole 7 and the auxiliary hole 9, thereby supporting the rotating body 11 on the balance testing machine 1 in a floating state and rotating the rotating body about the support journal 5 fixed in this state so that any unbalance force transmitted to the vibration bridge 4 is measured and the balance test is performed.
In this balance testing machine, in order to stably rotate the rotating body 11 about the support journal 5, it is necessary that a gap (a floating amount) between the plate 8 and the rotating body 11 is larger than a gap between the support journal 5 and the hole 12 in the rotating body 11. If the relation is reversed, the rotating body 11 rotates on the basis of a bottom surface 13 thereof, and it is impossible to perform a necessary measurement of unbalance amount.
Accordingly, viewing a pressure distribution of the compressive fluid such as the air or the like generating the floating force and acting on a portion between the bottom surface 13 of the rotating body 11 and the plate 8, first for simplifying, as shown in a graph in the middle of FIG. 2 showing a case where the outflow of the fluid from the auxiliary hole 9 is not generated, when the floating amount of the rotating body 11 is small, an area B by the gap between the plate 8 and the bottom surface 13 of the rotating body 11 is smaller in comparison with an area A by the gap between the support journal 5 and the hole 12, an inlet portion to the area B from the area A forms a nozzle, and a negative pressure portion 14 is generated by the occurrence of rapid expansion of the compressible fluid.
Accordingly, it becomes impossible to sufficiently float the rotating body 11 due to suction by the negative pressure portion 14. Hence, if the air supply pressure is raised, as shown in a graph in the bottom of FIG. 2, the negative pressure portion 14 rapidly disappears from a state shown by a broken line to a state shown by a solid line at the moment when the area A becomes smaller than the area B, and as a result, a sudden increase in the floating force occurs while causing the rotating body 11 to bound upward.
Further, in a case where the air or the like is allowed to flow out of the auxiliary hole 9 on the plate 8, as shown by a single-dot chain line in the graph in the bottom of FIG. 2, the floating force can be increased by increasing a pressure between the plate 8 and the bottom surface 13 of the rotating body 11, however, the air flowing out of the auxiliary hole 9 tends to flow toward an outer periphery of the plate 8 having a small resistance, and the above-mentioned negative pressure portion 14 is generated in the outer peripheral side of the auxiliary hole 9, so that in a heavy or a large size rotating body 11, there occurs a problem such that it is impossible to acquire a gap by a sufficient amount of floating force.
On the other hand, there can be considered an adoption of a non-compressive fluid such as a liquid, for example, a lubricating oil or the like is used instead of the compressive fluid of the gas such as the air or the like so as to prevent the nozzle effect from being generated, whereby the support of the weight of the rotating body 11 is made easy. Nevertheless, since a viscosity and a surface tension of the non-compressive fluid of the liquid are larger in comparison with the compressive fluid of the gas such as the air or the like, a rotational resistance caused by filling in a narrow gap between the support journal 5 and the hole 12 of the rotating body 11 becomes large, and a great rotating force is necessary for obtaining a necessary balance correction rotating speed. For example, in the configuration as shown in FIGS. 1A, 1B and 2, the fluid force for rotationally driving must become excessively large and accordingly, a problem is encountered in which the rotating body 11 tends to be eccentric with respect to the support journal 5.